Skin is the body's largest organ. About six pounds (about 2.7 kilograms) of skin cover eighteen square feet (1.67 square meters) on an average adult.
The top layer of skin is called the epidermis. It protects the underlying skin layers from the outside environment and contains cells that make keratin, a substance that waterproofs and strengthens the skin. The epidermis also has cells that contain melanin, the dark pigment that gives skin its color. Other cells in the epidermis allow us to feel the sensation of touch and provide the body with immunity against foreign invaders like germs and bacteria.
The very bottom layer of the skin is the hypodermis. It contains the fat cells, or adipose tissue, that insulate the body and help it conserve heat. The layer between the epidermis and the hypodermis is the dermis. It contains the cells that give skin strength, support, and flexibility. As a person ages, the cells in the dermis lose their strength and flexibility, causing the skin to lose its youthful appearance.
Located in the dermis are sensory receptors. They allow the body to receive stimulation from the outside environment and experience pressure, pain, and temperature. Small blood vessels provide the skin with nutrients, and remove its waste products.
Sebaceous glands produce the oil in the skin, which keeps it from drying out. The oil from the sebaceous glands also helps to soften hair and kill bacteria that get in the skin's pores. These oil glands are all over the body, except on the palms of the hands and the soles of the feet.
Review Date 8/22/2016
Updated by: Laura J. Martin, MD, MPH, ABIM Board Certified in Internal Medicine and Hospice and Palliative Medicine, Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.